Imagine being so exhausted, you can't summon the energy to stand up, make a cup of tea or walk along a road. Ian McAuley, 55, did not have to imagine.
A fortnight after catching a heavy flu in 2002, the teacher was racked with acute fatigue and muscle ache.
He did not know it at the time, but he was showing the early symptoms of Myalgic Encephalopathy (ME), otherwise known as chronic fatigue syndrome.
An estimated 250,000 people live with ME in the UK, a painful and debilitating neurological illness characterised by overwhelming exhaustion, sleep problems and joint and muscle pain.
In its most severe form, it can leave sufferers house or bed-bound for decades, with some having to be tube-fed.
When Ian was told by his doctor that there was no cure and that the condition was likely to stay with him for about two years, he went into shock.
"The thought of that being the minimum amount of time for the illness to run its course was quite trying," says Ian, who is head of humanities at Kelvin Hall School in Hull. "The severity varied from day to day. Sometimes I couldn't get up or drive short distances in the car."
In fact, it was more like three years before Ian started to feel better, but he is well aware that ME is unpredictable and could return at any point. During his illness, he made every effort to go to work as normal, although he had to have more non-contact time, which he spent sitting in a chair trying to recharge his batteries.
Action for ME, the charity and support group, is attempting to reach more men with the condition as part of this month's dedicated awareness drive.
Figures indicate that there are 80,000 men with the condition in the UK. A further 16,000 British men are thought to be undiagnosed - partly because they are less likely to go to the doctor, and partly because ME is wrongly considered a "female" illness. As such, it takes more than a year for 87 per cent of men with ME to be correctly diagnosed.
Ian was lucky enough to have an early diagnosis - a crucial factor for a quick recovery - but it was still a huge effort to stay on top of a notoriously tiring job.
"I was adamant that I didn't want to just sit at home while my classes had a succession of supply teachers," he says. "Most of my colleagues were very supportive and understanding, so it was just about manageable."
However, he did get some negative feedback, mostly from people who misunderstood the illness as solely psychological. "I got some comments like: 'We're all tired, what makes you so special?' while others made me feel like I was a burden on my colleagues. I do feel that a younger or less experienced teacher would have caved in and gone on long-term sickness leave, which would have meant a drop in salary."
Joint and muscle pain.
Digestive and bowel problems.
Difficulty with body temperature control.
A disturbing inability to understand, focus or concentrate.
The causes of ME are still unclear, although there are some predisposing factors:
Women are more prone to the condition than men.
About one in 10 people develop ME following a viral infection.
It can also be triggered by pesticides, vaccinations or toxins in the environment.
Physical injury or an operation can occasionally lead to ME.
Facts and figures
There are approximately 250,000 people living with ME in the UK.
About 25,000 people develop ME each year in Britain.
The illness usually develops between your early twenties and mid-forties, but can also affect children. See www.afme.org.uk or www.meassociation.org.uk.